1. Field of the Invention
This invention relates to a reaction apparatus to be used in the production of an alkanolamine, a method for production of an alkanolamine using the apparatus, a reactor, a method for charging the reactor with a catalyst, and a method for start-up of the production of an alkanolamine.
More specifically, it relates to a reaction apparatus to be used in producing a dialkanolamine by the reaction of ammonia, a monoalkanolamine, and an alkylene oxide in the presence of a solid catalyst, a method for selectively producing the dialkanolamine using the reaction apparatus, a reactor to be used in the production of an alkanolamine, a method for charging the reactor with a catalyst, and a start-up method for safe and efficient production of an alkanolamine using an adiabatic reactor in the presence of a solid catalyst by adjusting the temperature and the concentration of the raw material components during the contact between the raw materials and the catalyst.
2. Description of the Related Art
As a commercial approach to the production of an alkanolamine by the amination of an alkylene oxide with ammonia, the method which produces ethanolamine by the reaction of ethylene oxide with aqua ammonia (ammonia concentration in the range of 20-40 wt. %) has been in vogue. Though this method forms three species of amine, i.e. monoethanolamine, diethanolamine, and triethanolamine, it is required to repress the formation of triethanolamine among other species of amine because the demand for triethanolamine is decreased. The reaction, therefore, is generally carried out with the molar ratio of ammonia and ethylene oxide set at a large ammonia excess in the approximate range of 3-5. In spite of the effort, the selectivity of triethanolamine is in the range of 10-20 wt. % or more and the selectivity of diethanolamine is not more than 40% by weight.
In an anhydrous system, substantially no reaction occurs between an alkylene oxide and ammonia. For the reaction of this nature, therefore, a catalyst is indispensable. Thus, homogeneous catalysts such as organic acids, inorganic acids, and ammonium salts have been proposed (Swedish Patent No. 158,167). These homogeneous catalysts are difficult to be separated from the reaction system and fail to manifest fully satisfactory performance.
As an embodiment of the immobilization of such a homogeneous acid catalyst, an ion-exchange resin having a sulfonate group immobilized on resin has been proposed (U.S. Pat. No. 3,697,598). Since this catalyst manifests relatively good activity and selectivity, it has been already practiced on a commercial scale. The ion-exchange resin, however, entails the problem of having a low maximum working temperature. The ion-exchange resins which are commercially available generally have rather low maximum working temperatures of 120xc2x0 C. (xe2x80x9cIon Exchangexe2x80x94Introduction to Theory and Practicexe2x80x9d translated jointly by Rokuro Kuroda and Masami Shibukawa, published by Maruzen Co., Ltd., 1981, page 34). When ammonia and ethylene oxide are subjected to a reaction at a lowered molar ratio, the temperature of the catalyst bed is eventually compelled by the heat of reaction to exceed the heat resistant temperature. When the catalyst is used under these temperature conditions for a long time, it entails the problem of inducing deterioration of the catalyst. It is, therefore, difficult to lower the molar ratio of ammonia and ethylene oxide to a level in the approximate range of 20-25. With a view to overcoming the drawback of poor high-temperature resistance of the ion-exchange resin, an inorganic catalyst excelling in thermal stability has been studied.
U.S. Pat. No. 4,438,281 discloses silica alumina in popular use manifests a good catalytic activity.
Industrial and Engineering Chemistry, Product Research and Development, 1986, Vol. 25, pp. 424-430 publishes a comparative study performed between ion-exchange resins and various kinds of zeolite catalysts, etc. Particularly, in terms of the selectivity to a monoalkanolamine, no other substances used in this study surpassed ion-exchange resins.
U.S. Pat. No. 4,939,301 discloses acid activated clay catalysts. Some of these catalysts have manifested high yields of monoethanolamine of not less than 60% by weight. Since no catalyst has manifested a fully satisfactory selectivity to a monoalkanolamine, the reaction of ammonia and ethylene oxide is carried out with the molar ratio of these reactants increased to not less than 20-30 times the stoichiometric level. This reaction, however, is hardly practicable because the cost of equipment for recovering ammonia for cyclic use is prohibitive.
With a view to solving these problems, EP 652 207 A proposes use of a catalyst having a rare earth element carried on a heat-resistant carrier to produce a monoalkanolamine with a high selectivity. Since this catalyst is aimed at producing a monoalkanolamine with a high degree of selectivity, it is still deficient to produce a dialkanolamine.
A catalyst having a high degree of selectivity for a dialkanolamine can be obtained by using a microporous material having an effective pore diameter in the range of 0.45 to 0.8 nm or a catalyst obtained by subjecting this microporous material to an ion-exchange treatment and/or a surface treatment.
When the dialkanolamine further obtained by the use of this catalyst with a still higher degree of selectivity, the amount of the dialkanolamine ought to be increased theoretically by separating the monoalkanolamine formed in advance and recycling part of the separated monoalkanolamine to the reaction system. Neither an apparatus nor a method available for this method has been specifically disclosed, this method has a problem yet to be solved for the purpose of production to practice.
It has been known to produce an alkanolamine by the reaction of liquid ammonia with an alkylene oxide as disclosed in for example U.S. Pat. No. 3,697,598 and EP 652 207 A.
This production, when carried out on a commercial scale, however, has the possibility of inducing a channeling of the reaction mixture in the catalyst bed or an outflow of fine catalyst particles from the reactor.
For the purpose of preventing this channeling in a relatively large reactor, it needs to use a special catalyst packing device or a reactor of a complicated shape as described for example in JP-A-10-66,858, JP-A-07-60,102, JP-A-05-285,367, and PETROTECH, Vol. 20, pp. 960-965.
In recent years, with a view to overcoming the problem of heat resistance due to the use of such an ion-exchange resin, the feasibility of using an inorganic catalyst which excels in thermal stability under adiabatic conditions has been studied. EP 652 207 A for example, discloses catalyst for the production of an alkalolamine, which are characterized by carrying a rare earth element on a heat resisitant inorganic carrier. Since this catalyst itself carries heat resistance unlike an ion-exchange resin, the reaction can be carried out at a temperature of 50-300xc2x0 C., preferably of 80-200xc2x0 C. By using such a heterogeneous catalyst excelling in heat resistance, it is possible to increase the ratio of the alkylene oxide, improve the productivity of the reaction, and repress the ratio of ammonia to a low level, and thereby miniaturizing the reactor. Further, since the reaction temperature can be maintained at a high level, the efficiency of the reaction can be improved. In addition, the adiabatic reaction has an advantage that, when the reaction starts once, it continues the reaction by heat generated and ensures the sufficient rise of temperature necessary for performing the reaction promptly.
When the reaction of ammonia with an alkylene oxide is effected with the heterogeneous catalyst excelling in heat resistance under the adiabatic conditions between the exterior and the reactor, the interior of the reactor assumes an unstable state for a short while after the start-up. When the heterogeneous catalyst excelling in heat resistance is used, the ethylene oxide concentration can be maintained at a rather high level and the corresponding alkanolamine can be produced efficiently because the ratio of the ethylene oxide to ammonia can be increased. When the conditions remain in a stable state as described above, the alkanolamine can be produced in a constant quality because the reaction temperatures in the pre-heater and the reactor are stable and the molar ratio of the ethylene oxide to ammonia is stable as well.
In contrast, during the initial stage of the reaction which precedes to these stable conditions, the rapid production of the alkanolamine is difficult. Since the reaction is initiated at the time that the contact is established between the raw material components and the catalyst, the internal temperature of the reactor does not immediately rise uniformly after the introduction of the mixed liquid of raw materials, i.e. ammonia and the alkylene oxide, into the reactor with the catalyst. The internal temperature of the reactor does not rise to the highest reaction temperature till the mixed gas reaches the terminal end of the catalyst bed and thus the internal temperature has its distribution varied from the inlet toward the outlet, of the reactor. When the heterogeneous catalyst excelling in heat resistance is used particularly, the difference in temperature between the inlet and the outlet of the reactor is increased because the rise of temperature is large. When the temperature of the inlet of the reactor which is in a steady state is adopted at the time of start-up, not only the raw material substances are wasted because the alkylene oxide fails to react and the unaltered alkylene oxide copiously flows out of the reactor during the initial stage of the reaction but also the reaction possibly raises the problem of safety because the reactive alkylene oxide enters the ammonia recovery system. Further, if the product includes the unaltered raw materials in a large amount, it becomes difficult to produce the product homogeneously. The control of reaction temperature is difficult because the temperature of the catalyst is not stable. The rapid rise of the temperature during the start-up possibly entails dangers such as polymerization of a monomer component and blockage of the catalyst bed.
The mere increase of the ratio of ammonia to the ethylene oxide, however, brings such disadvantages as lowering the efficiency of the reaction and expanding the size of the reactor proportionate to the increase in the amount of ammonia as well.
When the catalyst such as the conventional ion-exchange resin which is deficient in heat resistance is used, the reaction temperature is low. This low reaction temperature is obtained by increasing the molar ratio of ammonia to the ethylene oxide to a level of not less than about 25. Under these conditions, even the adiabatic reaction brings only a small rise of temperature in the reactor. Thus, even when no special operation is made during the start-up or when the temperature in the catalyst bed is not uniform, neither any special inconvenience nor any noticeable hindrance is suffered to arise. The development of the heterogeneous catalyst excelling in heat resistance and reactivity, however, has forced the start-up preceding the stable state to encounter the problems mentioned above.
Even in a system without a catalyst, an alkylene oxide reacts with a monoalkanolamine or a dialkanolamine at a relatively large reaction rate. The reaction rate is nearly equal between the two species of amine or rather larger with the dialkanolamine. No selectivity exists for the formation of dialkanolamine. When the monoethanolamine is recycled with the object of obtaining the dialkanolamine by the reaction of ammonia with an alkylene oxide, the reaction of the alkylene oxide with the monoalkanolamine occurs before the arrival at the catalyst bed and consequently forms not only the dialkanolamine but also the trialkanolamine, with the problematic result that the selectivity of the dialkanolamine will be lowered and, at the same time, the amount of the triethanolamine will be increased.
As a result of a diligent study with a view to solving the problem, it has been found that the use of a reaction apparatus so constructed as to allow the mixing of the ammonia with a monoalkanolamine to preheat and supplying an alkylene oxide into the preheated fluid can suppress the by-production of triethanolamine. Consequently, the present invention has been achieved. The by-production of the triethanolamine can be further suppressed by the use of a reactor whose available volume from the feed inlet of the alkylene oxide to the entrance of the catalyst bed is not more than 0.5 times the volume of the catalyst bed in the reactor.
An object of the present invention is to provide a method for producing a dialkanolamine with a high degree of selectivity and an apparatus therefor.
The object mentioned above is accomplished by a reaction apparatus for producing a dialkanolamine with a high selectivity by causing ammonia and amonoalkanolamine to react with an alkylene oxide in the presence of a solid catalyst, which reaction apparatus is provided with a mixer for mixing ammonia with a monoalkanolamine, a pre-heater for preheating the fluid flowing from the mixer, an alkylene oxide mixer with a feed inlet for supplying an alkylene oxide and interposed between the pre-heater and a reactor for supplying an alkylene oxide via the feed inlet and mixing it into a fluid preheated by the pre-heater, and a reactor adapted to introduce the preheated mixture of ammonia, monoalkanolamine, and alkylene oxide flowing from the alkylene oxide mixer and with a catalyst bed packed with a solid catalyst.
The object mentioned above is further accomplished, in the production of a dialkanolamine with a high selectivity by the reaction of ammonia with a monoalkanolamine and an alkylene oxide in the presence of a solid catalyst, by a method for the production of a dialkanolamine which is characterized by supplying the alkylene oxide to a fluid obtained by mixing ammonia with a monoalkanolamine and preheating the resultant mixture.
The reaction apparatus of this invention is capable of repressing the conversion of a dialkanolamine into the trialkanolamine and allaying the degradation of the selectivity of the dialkanolamine.
The method of this invention is capable of repressing the conversion of a dialkanolamine into the trialkanolamine and allowing a dialkanolamine to be produced conveniently and efficiently.
The object of the present invention is, in view of the situation described above, to provide a reaction apparatus which prevents the solution from generating a channeling in the catalyst bed and prevents particles of the catalyst from flowing out of the reactor by a simple apparatus and a simple operation and a method for packing a catalyst.
The object mentioned above is also accomplished by a reactor for the production of an alkanolamine, which is characterized by having a honeycomb structure disposed inside the reactor.
Further, the object mentioned above is accomplished by a method for packing a reactor for the production of an alkanolamine with a catalyst, which method is characterized by disposing a honeycomb structure inside a reactor and packing the structure with a catalyst.
The object mentioned above is further accomplished by a method for packing an up-flow type reactor for the production of an alkanolamine with a catalyst, which method is characterized by packing a catalyst having a particle diameter of not more than 1 mm, superposing on the resultant catalyst layer inert particles having a particle diameter of 0.5 to 10 times that of the catalyst, and further superposing on the resultant superposed layer of the inert particles having a particle diameter of 1.5 to 10 times that of the inert particles.
By this invention, the following effects are attained.
1. Generally, in the reactor having a large diameter such as not less than 1 m, the resistance to flow path is smaller in the part of the catalyst bed lying along the lateral wall of the reactor than that among the catalysts. As a result, the raw materials in the reactor inevitably induce the phenomenon of flowing with deviation from the central part to the lateral wall side, of the reactor (column) i.e. the so-called channeling. This phenomenon is caused by the fact that the percentage of voids increases on the wall of the reactor and the fact that the catalyst is tightly packed in the central part.
In the so-called shell-and-tube type reactor, the pressure loss is substantially fixed and the channeling does not occur frequently when the catalyst beds are given a fixed length. While the heat-exchanger type reactor may well do by adopting a shell-and-tube type reactor, the adiabatic reactor cannot be adopted by reason of an inevitable high cost.
The use of the honeycomb structure contemplated by this invention permits formation of a state simulated to that of a shell-and-tube type reactor without appreciably changing the expense of the equipment.
2. The up-flow type reactor requires a catalyst retainer that prevents the catalyst from moving or flowing out. When the catalyst has a relatively large particle diameter, it can be retained with a metallic gauze. When the catalyst having very fine particles is used, the use of a metallic fine mesh gauze has the possibility that the catalyst will block the gauze.
When the inert particles are superposed on the catalyst bed and they have the same particle diameter as the catalyst, then the superposed layer of the inert particles does not function fully satisfactorily as a retaining means. When the inert particles to be used have an ample size for the purpose of retaining the catalyst, the catalyst leaks through the gaps between the adjacent inert particles and these individual retaining particles have an unduly large weight capable of harming the catalyst. This inconvenience can be avoided by superposing inert particles of gradually increased particle diameters.
3. The method for packing the reactor with the catalyst is relatively simple because the reactor can be packed with the catalyst after the honeycomb structure has been disposed in the reactor. Further, the honeycomb structure is a one-piece entity and can be easily disposed in the reactor. Since gaps are formed rarely between the honeycomb structure and the reactor, the fluid handled during the course of the reaction leaks or forms a short pass only rarely.
A further object of this invention is to provide a start-up method that is capable of initiating the production of an alkanolamine safely and efficiently.
The object mentioned above is accomplished by a startup method for the production of an alkanolamine by the reaction of ammonia with an alkylene oxide using an adiabatic reactor in the presence of a solid catalyst, which start-up method is characterized by initiating the reaction at an inlet temperature of the reactor higher than the prescribed temperature at an alkylene oxide concentration lower than the prescribed concentration and subsequently changing the inlet temperature and the alkylene oxide concentration gradually to the prescribed levels, respectively.
When the start-up method according to this invention is carried out, the temperature of the catalyst bed can be maintained at a high level from the beginning of the start-up operation by supplying ammonia at a temperature higher than the prescribed temperature to the reactor (the curve of 17 minutes in the diagram of FIG. 8 to be described below). When the reactor is externally heated, it requires a separate apparatus. In the present invention, however, the inlet temperature of the reactor can be readily heightened by using an adiabatic reactor with a pre-heater that is normally disposed in any apparatus of this class (FIG. 8 to be described below). In this respect, in the operation which produced the results depicted in FIG. 9, the degree of conversion of ethylene oxide was low and the unaltered ethylene oxide flowed out of the reactor because the temperature of the catalyst was not raised fully during the initial stage of reaction and the temperature of the reactor barely began to rise after the elapse of 30 minutes.
Since the alkylene oxide of a rather low concentration is supplied and this concentration is subsequently elevated gradually after the temperature of the reactor has been raised, the alklene oxide so supplied can acquire the reactivity at a sufficiently high catalyst temperature and no unaltered alkylene oxide occur at the outlet of the catalyst bed. Thus, the product of high quality can be obtained with high efficiency because it is not necessary to remove unaltered raw materials from the product. The favorable outcome of this operation maybe logically explained by a supposition that, as clearly noted from FIG. 10 which will be described below, the start-up can be stably implemented even under such conditions that the molar ratio of the alkanolamine to ammonia may be as low as 8 and the ethylene oxide concentration may be high.
According to the start-up method of this nature, the elevation of temperature cannot occur rapidly because the temperature of the catalyst bed is gradually elevated by the heat of reaction. Even when the steady operation is carried out at a high alkylene oxide concentration by the use of a heterogeneous catalyst excelling in heat resistance, the possibility of this operation entailing polymerization of a monomer component and blockage of a catalyst bed due to an abrupt change of temperature during the course of the startup operation is nil.
The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments.